Monday, October 10, 2011

Fixing Salvinia Issues at Gunn, Palmerston, NT

Salvinia is a nasty, super spreading – even choking – weed.

Over the past few years an infestation has been developing at the lakes at Gunn, in Palmerston, and is now quite significant, covering the lakes [ see lowest lake below]. The lakes are designed as a stormwater buffer, so water levels can rise and fall quite a lot in the wet season.

Late last year Palmerston City Council instigated using their aquatic weed muncher to remove much of the debris across these lakes. Unfortunately, some salvinia remained.

A program which we ran, was used to spray and mop up the balance. That was the theory...... but then it rained and rained, with last wet season being extraordinarily wet, and consistently wet. Too wet for regular satisfactory spraying.

So the salvinia regrew.......and once again dominated the three lakes.

The weed eater is back in action , and the upper lake is now quite clear of salvinia, with the two lower ones likely to be cleaned up this week.

But there is a new activity........the salvinia weevil, a very potent biocontrol agent has today been released into the bottom lake with additional material to be added over the next few weeks in both the lowest and middle lakes, with some destined for the top lake as needed. Biocontrol of salvinia has been very successful at a number of locations around both Australia and in the Northern Territory.

To aid establishment a small amount of salvinia plants will be left behind during the weed munching, to provide a focus for the spread of the biocontrol agent, and these plants will be held in place with a floating boom. Over time, assuming the biocontrol agent establishes successfully, this plant mat will also disappear, and the weevil will spread out onto any remnant salvinia around the lakes.

The biocontrol agent will not necessarily totally eliminate the salvinia, but it will normally, over some time, reduce the salvinia to a small, almost negligible amount.

A monitoring, spray and clean up / collection program will also continue, but concentrating on the smaller scattered fronds that seem to congregate around the edges, readily blown by wind.

This combined program is hopeful of eliminating the salvinia over the next 12 months, and at worse, at least reducing the salvinia to a very minor issue.

The lakes may then bloom again with the stylish water lilies that are quite common, and salvinia will not be very noticeable.